In recent years, individuals have increasingly been made aware of the advantage of vigorous exercise, including its beneficial effect on the heart, as well as nuscle tone in general. As a result of this awareness, long distance jogging, for example, has become very popular, particularly among individuals wishing to be involved in outdoor activities, and at the same time, wanting to enjoy the benefits resulting from strenuous physical exertion.
Many of those engaging in the sport, and other activities requiring prolonged and intense movement of the legs and feet have unfortunately become aware of the fact that such exercise can result in painful injuries and afflictions. For example, "shin splints," painful straining of the extensor muscles in the lower leg resulting from running on a hard surface can be developed. In addition, planter fasciitis, a hurtful inflammation of the tissue on the bottom of the foot can be experienced, as well as a malady involving "jamming" of the large toe, commonly referred to as "turftoe."
As might be imagined, a wide variety of sports equipment has been developed to facilitate running-related activities. This is particular true in the case of athletic footwear such as specially designed running shoes which frequently employ board last, or slip last construction, or combinations thereof to reduce the weight of the shoes. With respect to athletic shoes, the objective has been to make the shoes as light as feasible to minimize the energy required in exercising in them to the extent possible. To further reduce the shoe's weight, lighter-weight construction materials such as ethylene, vinyl acetate, nylon, polyurethane, and various other synthetics have been employed in their fabrication. The shoe designs achieved, however, have necessitated a compromise insofar as the wearer is concerned, inasmuch as while lighter footwear reduces the amount of energy expended, the weight loss has been achieved at the cost of the shoe's structural stability.
Stability of an athletic shoe is a matter of no minor importance since the manipulation of an individual's foot during walking or running places a significant torsional force on the shoe, relative to its longitudinal axis. Unless the twisting thus imposed is resisted, it tends to result in pronation, or supination, i.e., a "rolling in" or a "rolling out" of the shoe and the foot of the wearer. In many cases, such a result tends to exacerbate the physical conditions referred to above. In addition, the excessively flexible construction of the lighter shoes interferes with the rigidity needed to permit efficient propulsive foot movements by the wearer.
The problem of making athletic shoes lighter, and at the same time making them physically sturdy has been recognized for some time, and a variety ways have been proposed for simultaneously achieving both objectives.
One such approach is that described in U.S. Pat. No. 4,484,397, involving the control of a running shoe by means of a horizontal, somewhat "U"-shaped device consisting of an upper flange, for example, partially fitting over a heel wedge member, and connected by an extending sidewall to a lower flange fitting partially between the heel wedge and the lower midsole member. The rigid spacing of the flanges is intended to prevent compression of the heel wedge when the midsole compresses as the runner's foot rolls inward, in a manner intended to prevent pronation. The device suffers from its complexity, however, as well as from the fact that by preventing compression of part of the sole member, a harder foot support results, further aggravating some of the problems referred to.
Another device for reducing pronation and supination is described in U.S. Pat. No. 4,459,765, entailing a resilient heel member bonded to the exterior of the shoe which provides both vertical and longitudinal support and bracing. While the device may be effective with respect to the heel portion of the shoe, the corrective structure involves the drawback that it has minimal, or no effect on the equally important portions of the shoe distal to the heel, and that it provides no torsional reinforcement.
Still another approach suggested is that shown in U.S. Pat. No. 4,759,136 which makes use of a shoe that includes a midsole having a relatively soft central portion, and a peripheral portion of intermediate hardness extending around the central portion in the region of the heel and forward along each side of the shoe to the toe region. Although claiming to avoid overpronation and oversupination, the device makes no provision for torsional reinforcement.
An additional proposal is that disclosed in U.S. Pat. No. 4,625,435, which involves a device for preventing rolling of the heel portion of an athletic shoe. The device consists of an inverted "T" shaped plate whose horizontal inner flange is adapted for insertion between the shoe's upper and the shoe's sole. However, the device is without structure that would prevent torsional twisting, and is configured in a way that would beneficially affect only the heel of the shoe.
U.S. Pat. No. 4,288,929 shows a tray-like roll control device with upwardly sloping walls intended for placement in the heel portion of an athletic shoe. No protection is afforded to the frontal region of the foot, however, and even the torsional reinforcement in the heel area would be relatively marginal.
Other approaches have involved multiple layer midsoles of differing densities, U.S. Pat. No. 4,694,591; multiple component heel members of differing densities U.S. Pat. No. 4,730,402; horseshoe-shaped heel structures, U.S. Pat. No. 4,490,928; shoes with a peripheral sole portion having one density, and an inner sole portion of a different density, U.S. Pat. No. 4,302,892, and a variety of others. While all of the devices are designed to provide support of one type or another, none offer the torsional support provided by the invention disclosed herein, and none are designed to protect the area of the foot which this invention contemplates.